1. Field of the Invention
The present invention relates to a thermal printer and electromagnetic wave source device. More particularly, the present invention relates to a thermal printer in which images on thermosensitive recording material are fixed by a photo fixer with electromagnetic rays, and efficiency in the fixation can be prevented from influence of degradation of the photo fixer, and electromagnetic wave source device for emitting such electromagnetic rays.
2. Description Related to the Prior Art
A color thermal printer of a direct printing type is known, and used with color thermosensitive recording material. The recording material includes a support and three thermosensitive coloring layers overlaid thereon for primary colors. The coloring layers are a first, second and third coloring layers in an order toward the support. The first coloring layer has the highest heat sensitivity, and develops its color in response to application of relatively low heat energy. The third coloring layer has the lowest heat sensitivity, and develops its color in response to application of relatively high heat energy. The coloring ability of the first and second coloring layers is destroyed upon application of visible or ultraviolet rays with particular wavelengths. When the recording material is transported, a thermal head is operated to heat and pressurize the recording material, the thermal head extending in a direction crosswise to the transport. So colors are developed in the coloring layers by the thermal recording. After this, a photo fixer is operated to apply violet or ultraviolet rays to the recording material. Before printing to the second coloring layer, the first coloring layer is fixed electromagnetically. Before printing to the third coloring layer, the second coloring layer is fixed similarly. This is to suppress further development of the colors in the first and second coloring layers after intended coloring.
As an electromagnetic wave source for the photo fixer, a mercury fluorescent lamp of a straight tube type is used widely. The mercury fluorescent lamp includes a glass tube and a pair of electrodes. The glass tube is provided with gaseous mercury enclosed therein, and has fluorescent film that is a coating of phosphor. The electrodes are located at ends of the glass tube. When electric current flows to the electrodes, thermal electron is emitted from the electrodes. The electron excites the gaseous mercury to generate ultraviolet rays. The phosphor receives the ultraviolet rays, and responsively violet or ultraviolet rays are emitted to the outside. It is possible with the mercury fluorescent lamp to emit rays continuously. This is typically because energy efficiency of the mercury fluorescent lamp is comparably high. The phosphor in the mercury fluorescent lamp can be constructed in a manner suitable for continuous emission of rays.
However, it is well-known that degradation occurs in the mercury fluorescent lamp to lower an amount of electromagnetic rays after long use. If high energy is applied to the mercury fluorescent lamp in this state, no strong rays are emitted. To compensate for this low performance in view of sufficient fixation, it is necessary to lower a feeding speed of the recording material relative to the mercury fluorescent lamp. This control of changing the feeding speed has problems in elongation of the time required for the photo fixation, to cause low efficiency in the printing operation.